1. Programming Language Principles
Extending Tiny
Programming Language Principles
Lecture 19
Prepared by
Manuel E. Bermúdez, Ph.D.
Associate Professor
University of Florida

2. Extending Tiny Let's add a few more constructs to Tiny.
The repeat statement (a la Pascal).
Code:
n: E1 E2
iffalse n

3. The Repeat Statement (a la Pascal)
E → <repeat E E >
code () = gen(code (2), "iffalse",next ())
next () = next (2) + 1
top () = top (2) - 1
error () = if type (2)="bool"
then error (2)
else gen(error (2), "non-bool exp")
type () = "statement"

5. Extending Tiny (cont’d)
The one-armed "if".
Code: E1
iffalse n E2 n:

6. The One-Armed "if" E → < if E E >
code (2) = gen(code (1), "iffalse",next (2))
next (2) = next (1) + 1
top (2) = top (1) - 1
error (2) = if type (1)="bool"
then error (1)
else gen(error (1), "non-bool exp")
type () = "statement”

8. Extending Tiny (cont’d)
Conditional Expression
Code: E1
iffalse n E2
goto m
n: E3 m:

9. Conditional Expression
E → < cond E E E >
code (2) = gen(code (1), "iffalse",next (2)+1)
next (2) = next (1) + 1
top (2) = top (1) - 1
error (2) = if type (1)="bool"
then error (1)
else gen(error (1), "non-bool exp")

10. Conditional Expression (cont’d)
code (3) = gen(code (2), “goto",next (3))
next (3) = next (2) + 1
error () = if type (2)= type (3)
then error (3)
else gen(error (3), “type mismatch")
top () = top (3) - 1
type () = type (2) ??? type (3) ???

12. Extending Tiny Prefix auto-increment.
Problematic. If x has not been defined, what location do we reserve for it on the stack ?
Code:
load n
lit 1
add
save n
load n n = lookup(x)

13. Prefix Auto-Increment
E → < ++p ‘<identifier:x>’ >
code () =
if lookup(x)=0 then code ()
else gen(
gen(
gen(code (), "load", lookup(x)),
"lit", 1),
"add"),
"save", lookup(x)),
"load", lookup(x))

14. Prefix Auto-Increment (cont’d)
error () = if lookup(x) !=0
then error ()
else gen(error (), "var undefined")
next () = next () + 5
top () = top () + 1 ???
type () = ???

16. A Sample "Compilation" Using Tiny's AG
To save time (and space), we'll track only code, next, top

17. A Sample "Compilation" Using Tiny's AG (cont’d)
Tiny program:
program teeny:
assign x := read;
if x=1
then assign x:=0
else output x end
teeny.
Code file:
read
load 1
lit 1
equal
iffalse 9
lit 0
save 1
goto 11
print
stop.

19. Programming Language Principles
Extending Tiny
Programming Language Principles
Lecture 19
Prepared by
Manuel E. Bermúdez, Ph.D.
Associate Professor
University of Florida